1. Field of the Invention
This invention relates to a disposable syringe having a means for retracting the needle into a barrel after use in a manner which avoids personal contact with the needle type.
Cutaneous punctures by used needles are common occupational injuries for health care personnel. Of particular concern is the risk these workers incur of contracting a systemic disease such as Serum Hepatitis or Acquired Immunodeficiency Syndrome.
Most needle-stick injuries occur during disposal of used needles. The injury risks associated with simply recapping a hypodermic needle after use is sufficiently great for some institutions to discourage their personnel from recapping used needles.
Installing a new needle on the end of a syringe in preparation for use is generally quite safe and easy in that needles are generally packaged in solid plastic sheaths or in some other similar manner that covers the needle point until the needle is securely installed on the syringe. Thus, the plastic sheath or the like can be safely grasped and the needle can be securely affixed onto the end of the syringe, either by friction or by twisting the needle onto a "Luer" connection.
2. Description of the Related Prior Art
Disposable syringes having a means for retracting the needle into the barrel of the syringe are well known in the prior art. U.S. Pat. No. 4,026,287, issued May 31, 1977, to Irene Haller discloses a syringe having a piston 36 provided with a tapered surface which includes an engaging means formed as a thread for selective engagement with a threaded recess provided in the end wall of a barrel, the end wall supporting a needle. Subsequent to engagement between the thread and threaded recess, retraction of a plunger attached to the piston causes the end wall to break along frangible serrations so as to allow the needle to be withdrawn within the barrel. There is no disclosure in Haller of internal threads at either end of the barrel whereby the needle may be secured in either the extended position or the retracted position as desired by engagement between a flange on said needle and said internal threads.
U.S. Pat. No. 4,995,874, issued Feb. 26, 1991, to H. Allen Strickland similarly discloses a plunger 12 having a piston 14 positioned for axial movement within a cylinder 16 and having a tapered threadlock 18 engageable with a threadbore 26, whereby subsequent to engagement, needle 32 is withdrawn into the cylinder. Strickland does not disclose a cylinder having internal threads at either end provided for the purpose of securing the needle at either end of the cylinder.